A maceral is a component, organic in origin, of

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitut ...

. The term 'maceral' in reference to coal is analogous to the use of the term '

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

' in reference to

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

rocks. Examples of macerals are

inertinite Inertinite is oxidized organic material or fossilized charcoal. It is found as tiny flakes within sedimentary rocks. The presence of inertinite is significant in the geological record, as it signifies that wildfires occurred at the time that the ho ...

, vitrinite, and liptinite.

Inertinite

Inertinite is considered to be the equivalent of charcoal and degraded plant material. It is highly oxidised in nature and may be said to be burnt. A large portion of South Africa's coal reserves consist of inertinite.

Vitrinite

Vitrinite is shiny, glass-like material that is considered to be composed of cellular plant material such as roots, bark, plant stems and tree trunks. Vitrinite macerals when observed under the microscope show a boxlike, cellular structure, often with oblong voids and cavities which are likely the remains of plant stems. This has a high calorific value (24 - 28 MJ/kg) and a large proportion of volatile matter (24 - 30%). It often occurs interbanded or interlaminated with inertinite and can be recognised as bright bands.

Liptinite

Liptinite macerals are considered to be produced from decayed leaf matter, spores, pollen and algal matter. Resins and plant waxes can also be part of liptinite macerals. Liptinite macerals tend to retain their original plant form, i.e., they resemble plant fossils. These are hydrogen rich and have the highest calorific values of all coal macerals. Macerals of liptinite are sporinite,

cutinite Cutinite is a liptinite maceral formed from terrestrial plant cuticles, and often found in coal deposits. It is classified as a Type II kerogen. References Coal Petrology {{petrology-stub Cutinite is a coal maceral of Liptinite In coal geolog ...

, resinite,

alginite Alginite is a component of some types of kerogen alongside amorphous organic matter. Alginite consists of organic-walled marine microfossils, distinct from inorganic (silica)-walled microfossils that comprise diatomaceous earth. Alginite is a com ...

( telalginite and lamalginite), liptodetrinite, fluorinite, and

bituminite Bituminite is an autochthonous maceral that is a part of the liptinite group in lignite, that occurs in petroleum source rocks originating from organic matter such as algae which has undergone alteration or degradation from natural processes such ...

Nature of macerals

Macerals are considered to be dehydrogenated plant fragments. Evidence for this includes remnant

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

, fossilised leaves, remnant cellular structure and similar. In rare cases, maceral and fossilised pollen can be found in terrestrial sedimentary rocks. Maceral maturity can be estimated by ''vitrinite reflectance''. This gives information on the carbon, hydrogen and nitrogen composition of the coal, and determines the type of coal:

lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...

brown coal Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...

bituminous coal Bituminous coal, or black coal, is a type of coal containing a tar-like substance called bitumen or asphalt. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the seams. It ...

anthracite Anthracite, also known as hard coal, and black coal, is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the hig ...

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...

. Macerals found in

kerogen Kerogen is solid, insoluble organic matter in sedimentary rocks. Comprising an estimated 1016 tons of carbon, it is the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. It ...

source rocks are often observed under the microscope to determine the kerogen maturity of the sedimentary formations. This is a vital component of oil and gas exploration. Macerals are observed under the

petrographic microscope A petrographic microscope is a type of optical microscope used in petrology and optical mineralogy to identify rocks and minerals in thin sections. The microscope is used in optical mineralogy and petrography, a branch of petrology whi ...

under reflected light. Coal fragments must be extremely highly polished down to less than half a micrometre before they can be observed under the microscope.

External links

Maceral identification

Maceral Tutorial
Petrology Coal {{geology-stub

Inertinite

Vitrinite

Liptinite

Nature of macerals

See also

External links